/*
 * Copyright (c) 2018 Zilliqa
 * This source code is being disclosed to you solely for the purpose of your
 * participation in testing Zilliqa. You may view, compile and run the code for
 * that purpose and pursuant to the protocols and algorithms that are programmed
 * into, and intended by, the code. You may not do anything else with the code
 * without express permission from Zilliqa Research Pte. Ltd., including
 * modifying or publishing the code (or any part of it), and developing or
 * forming another public or private blockchain network. This source code is
 * provided 'as is' and no warranties are given as to title or non-infringement,
 * merchantability or fitness for purpose and, to the extent permitted by law,
 * all liability for your use of the code is disclaimed. Some programs in this
 * code are governed by the GNU General Public License v3.0 (available at
 * https://www.gnu.org/licenses/gpl-3.0.en.html) ('GPLv3'). The programs that
 * are governed by GPLv3.0 are those programs that are located in the folders
 * src/depends and tests/depends and which include a reference to GPLv3 in their
 * program files.
 */

#ifndef __SINGLETON_H__
#define __SINGLETON_H__

template <typename T>
class Singleton {
 protected:
  Singleton() noexcept = default;

  Singleton(const Singleton&) = delete;

  Singleton& operator=(const Singleton&) = delete;

  virtual ~Singleton() = default;  // to silence base class Singleton<T> has a
                                   // non-virtual destructor [-Weffc++]

 public:
  static T& GetInstance() noexcept(std::is_nothrow_constructible<T>::value) {
    // Guaranteed to be destroyed.
    // Instantiated on first use.
    // Thread safe in C++11
    static T instance;

    return instance;
  }
};

#endif  // __SINGLETON_H__
